The present disclosure relates to a battery having a plurality of battery cells for making available an electrical output voltage and battery electronics which are coupled to the battery cells and which comprise current measuring means for determining a present battery current, detection means for determining further operating parameters of the battery cells, and setting means for setting an excess current threshold for the battery current by means of an actuation variable. In addition, the disclosure relates to a corresponding method for safely operating a battery having a plurality of battery cells, in which method, during the operation of the battery, a present battery current and further operating parameters of the battery cells are determined by means of battery electronics which are coupled to the battery cells, and in which an excess current threshold for the battery current is set by means of an adjustable actuation variable.
It is clear that in the future batteries with a high power density and stringent safety requirements will be used increasingly not in the automotive sector but also in stationary applications and in the consumer sector. Possible batteries for these purposes are, in particular, batteries which are based on lithium-ion technology and which are distinguished not only by a high energy density and power density but also by a low level of self-discharging.
In order to ensure the reliability and a long service life of the batteries, suitable battery monitoring electronics have been developed with which operating parameters of the battery, such as the cell voltage, state of charge, temperature, charge current and/or discharge current are measured and are monitored. In this context, in the case of batteries, in particular the measurement of the battery current, both in the determination of the state of charge and also the measures to ensure safe operation, is considered to be particularly important. This is due, inter alia, to the type of hazards which can give rise to an inadmissible current. For example, an overload of the battery during which more current is made available by the battery than the instantaneous state of the battery permits, taking into account, for example, the present temperature or the state of health of the battery, can lead to dangerous overheating of the battery. An excess current in which more current is made available by the battery than the individual battery cells can supply in accordance with their specification can also lead to resulting dangerous overheating.
A particularly critical point of the monitoring of battery currents is monitoring of the charge current at low temperatures. For example, charging with high currents at very low temperatures can result in the deposition of metallic lithium, which can lead to a considerable malfunction of the battery. The associated monitoring of this so-called “lithium plating” is particularly critical since even a few amperes too many can lead to an undetected fault in the battery.
In order to reliably measure a battery current and in order to allow for the safety classification which is required according to ASIL C (ISO26262) and which arises as a result of the danger and risk analysis mentioned above, particular measures are conventionally taken: accordingly, additional monitoring hardware is often arranged on a current sensor, which hardware is implemented, for example, by means of comparators and which triggers at a certain excess current. Another frequent variant with which multi-channel measurement is ensured is to use two different current sensor systems in one battery, involving the use of, for example, a Hall sensor and a shunt-based sensor at the same time.
US 2011/02416 A1 also specifies a protection device for protecting a load circuit of a battery, in which an excess current threshold is adjusted as a function of the battery voltage.